R-Matrix study of the β⁺decay of ⁸B to the highly excited states of ⁸Be

Abstract

Experiment IS633 was conducted at the ISOLDE facility with the aim of studying the 2+ isospin doublet of 8Be, the only expected case of nearly equal isospin configuration mixing. The doublet was previously probed by reaction studies where the feeding does not depend on the isospin. Beta decay studies are sensitive to the isospin composition of the doublet since the Fermi and Gamow-Teller strengths are heavily dependent of isospin. In this experiment the doublet was probed through the EC/β+ feeding from 8B. A four-particle telescope setup with a C-foil in the centre was employed to stop the 8B beam, the implanted nucleus would decay and populate the doublet that breaks up in two alpha particles that are detected. The statistics achieved in this experiment were two orders of magnitude higher than that of any previous experiment, enabling the first experimental observation of both contributions to the doublet.